Optical or electrical frequency combs consist of a series of essentially equidistant electrical pulses which are approximately shaped as Dirac delta functions. These electrical frequency combs are often used for phase and amplitude calibration of spectrum analyzers or oscilloscopes, wherein the electrical combs serve as a known reference for the calibration process.
For the generation of the reference frequency comb, there are two seemingly contradictory requirements. On one hand, a certain minimum signal-to-noise ratio is required which is linked to a minimum power level of the electrical frequency comb. The power level of the electrical frequency comb in turn is determined by the number of pulses per time interval, e.g. the pulse frequency in time domain. A high power level therefore demands for a high pulse frequency in time domain.
On the other hand, usually a very fine frequency comb is desired, e.g. the frequency interval between peaks in the frequency domain should be very small. This, however, corresponds to a large time interval between peaks in time domain as the intervals in time and frequency domain are inversely proportional to each other. Thus, a fine frequency comb in frequency domain requires a low pulse frequency in time domain.
Therefore, there is a need for a frequency comb generating device as well as a method for generating an optical or an electrical frequency comb that are capable of generating fine frequency combs with a high signal-to-noise ratio.